1. Field of the Invention
The present invention concerns railroad braking systems. More particularly, the invention relates to an air distribution apparatus configured for retrofit with an existing airbrake valve to act as an interface with an electronic braking control device.
2. Description of the Prior Art
A typical prior art braking system for a railroad car includes a control valve, a dual chamber air tank, a brake cylinder and distribution piping. Operating air is supplied from the railroad locomotive to the cars by way of a brake pipe that runs along the length of the train with the coupling between cars being in the form of rubber hoses. To those skilled in the art, the control valve is known generically as an "AB" valve, which is produced as various models such as an ABDW valve, and includes an service portion, an emergency portion and a pipe bracket portion therebetween. The air tank chambers include an auxiliary reservoir and an emergency reservoir.
During startup, supply air received from the brake pipe is distributed by the control valve to the two reservoirs until sufficient pressure has built up. In operation, the engineer activates a valve in the locomotive to cause a drop in the brake pipe pressure. The service portion of the control valve responds to the pressure drop as an air signal to distribute air at a pressure corresponding to the air signal from the auxiliary reservoir to the brake cylinder. In other words, the amount of braking force to the car is proportional to the drop in pressure in the brake pipe. For example, the brake pipe is normally pressurized at about 90 psi and a pressure drop of about 20 psi is a signal to the control valve to supply full braking pressure from the auxiliary reservoir to the brake cylinder.
In the event of a sudden, substantial pressure drop (in excess of 20 psi) in the brake pipe, the emergency portion of the control valve delivers full braking pressure from the emergency reservoir to the brake cylinder. Such might occur, for example, when a car becomes disconnected from the rest of the train, which vents all of the air pressure from that section of the brake pipe.
As those skilled in the art appreciate, the prior art braking systems present a number of problems. For example, the air pressure signal initiated in the engine propagates along the brake pipe at the speed of sound. With a long train, the cars in the front of the train are braked sooner than the cars in the rear, resulting in "run in." Another problem is that all of the cars are braked with the same braking force proportional to the brake pipe signal regardless of variations in the weight of the car. This means that an empty car will slow down more quickly resulting in run in and in extreme cases could result in locked wheels with the attendant damage and wear, and possible derailment.
In response to these problems, some prior art solutions have proposed an electronically controlled braking system in which wireless signals from the engine are transmitted to respective receivers on the cars. This effectively eliminates propagation delay and allows onboard, individualized, electronic control of the braking of each car. These prior art electronic braking systems, however, are not adapted to operate compatibly with conventional air brake systems. As a result, all of the cars of the train must be electronically equipped, which makes economic conversion impractical.